1. Field of the Invention
The present invention relates to a secure system for controlling the unlocking of at least one openable panel of motor vehicles.
2. Description of the Related Art
In the remote control systems currently used for unlocking motor vehicle doors, the user has to manually actuate his remote control (transponder built into the gripping part of his mechanical key) so as to actuate the unlocking of the doors.
Now, for greater user comfort, one wishes to do away with manipulations of this type.
So-called xe2x80x9chands-freexe2x80x9d systems have recently been proposed, in which the user carries a transponder which is for example built into a badge. This transponder comprises, on the one hand, capacitive means which are charged when the said reception/transmission means receive a radio-frequency radiation and, on the other hand, an antenna into which the said capacitive means are discharged when this radiation disappears. On receiving a radio-frequency interrogation signal transmitted from the vehicle, the transponder itself transmits a radio-frequency identification signal in response. When this signal is received and identified by means provided for this purpose on the vehicle, these means control the unlocking of the openable panel.
Such a system is totally transparent to the user, since the unlocking of the doors is controlled without the user having to perform operations other than that consisting in his manipulating the handle of his door.
However, such xe2x80x9chands-freexe2x80x9d systems pose security problems.
In particular, certain xe2x80x9cill-intentionedxe2x80x9d persons may copy the interrogation signal transmitted from the vehicle so as to retransmit it near to the transponder, even were the user carrying this transponder to be located somewhere far from the vehicle. By employing suitable means near to the user, they store the identification signal transmitted in response by the transponder and retransmit this signal in the vicinity of the vehicle so as to obtain the unlocking of the latter""s doors.
An aim of the invention is to propose a solution making it possible to prevent deceptions of this type.
The invention therefore proposes a system for controlling means for locking/unlocking at least one motor vehicle openable panel comprising transmission/reception means which are intended for transmitting, from the vehicle, a radio-frequency interrogation signal, which transmission/reception means are intended to be carried by a user and which, on receipt of the interrogation signal, are intended for transmitting a radio-frequency identification signal so as to actuate the unlocking of the openable panel, which system comprises detection means which are linked to the transmission/reception means on the vehicle and which are able to detect, on an identification signal received on the transmission/reception means, a modification of a parameter of the transmission, between the transmission/reception means of the vehicle and of the user, which may be due to the interposition, between the vehicle and the user, of intermediate transmission/reception means.
In particular, according to an advantageous embodiment, the transmission/reception means intended to be carried by the user consist of a transponder comprising capacitive means which are charged when the said transmission/reception means receive a radio-frequency radiation, as well as an antenna into which the said capacitive means are discharged when this radiation disappears and the detection means comprise means for detecting on an identification signal received on the transmission/reception means, a modification of a parameter of the transmission chain which carries out the transmission of the interrogation signal from the vehicle, its reception by the transponder, the transmission of the identification signal by the transponder and its reception on the vehicle.
Such a system is advantageously supplemented with the various following characteristics taken alone or according to all the technically possible combinations:
the interrogation signal transmitted from the vehicle is a signal which is split on at least two frequencies.
at least a part of the signal transmitted from the vehicle is modulated in amplitude and/or in phase and/or in frequency with a pseudo-random code.
the system comprises, on the vehicle, means able to determine a modification of a frequency signature on the identification signal received.
the system comprises, on the vehicle, means able to determine a modification of an impulse signature on the identification signal received.
the system comprises, on the vehicle, means for determining the correlation function between the interrogation signal and the identification signal received.
the system comprises means for analyzing the shape of the correlation function so as to detect the interposition of intermediate transmission/reception means between the vehicle and the user.
the system comprises means for calculating the Fourier Transform of the correlation function and for determining, as a function of this Fourier Transform, the passband of the signal transmission chain.
the system comprises, on the vehicle, means able to determine a delay on the identification signal received.
the system comprises means for determining the delay by which the interrogation signal must be shifted as appropriate to obtain a correlation peak.